The juice extraction process is well known to those skilled in the art, such as described in U.S. Pat. No. 5,992,311, assigned to the present assignee, the disclosure of which is hereby incorporated by reference in its entirety. A fruit, vegetable and the like is fed to a juice extractor, which acts as the primary extractor, and produces a pure liquid (juice) and a fibrous material (pulp) from fruit, vegetables and the like.
After extraction, the mixture of juice and pulp is fed as a stream into a pulp concentrator, which is designed to separate a substantial amount of juice from the pulp and to adjust the concentration, or dryness, of the pulp to a desired range. The pulp concentrator may consist of a finisher, which may include a screw type finisher, paddle type finisher, centrifugal type finisher or decanter. The pulp concentrator may also consist of a rotary screen, vibrating screen or other type of separating device as readily appreciated by those skilled in the art.
The screw type and paddle type finishers, for example, rely on the juice to be extruded through a screen material, which regulates the size of the pulp that is maintained within the juice stream. Any pulp that is too large to be extruded through this screen is compressed by centrifugal and mechanical force, which is created by limiting the flow of pulp discharge either by a back pressure regulator and/or a weighted gate.
The juice that is separated from the pulp concentrator is further processed by pasteurization or evaporation as readily appreciated by those skilled in the art. The pulp that is separated from the pulp concentrator has various uses. In some juice processing facilities, this pulp is considered waste or is added to other fruit waste and processed into animal feed. In other juice processing facilities, this pulp is considered a valuable by-product and can either be used for pulpwash or collected as pulp cells. When used for pulpwash, the pulp is washed with water to recover juice solids, such as natural sugars, that are present in the pulp. When collected as pulp cells, the pulp from the concentrator is typically pasteurized to reduce the amount of natural occurring microorganisms prior to packaging, storage or use. Pulp cells may be added back to juice or used as an ingredient in other foods or beverages. When pasteurizing pulp, it is critical to maintain the concentration, or density, of the pulp during pasteurization.
Problems arise, for example, when a pulp pasteurizer is fed with a concentration of pulp less than optimum. The energy for both heating and cooling is increased on a per ton basis of processed material discharged by the pulp pasteurizer in the form of packaged pulp material. Besides having a higher energy cost to produce the product, the final product can be out of density specification. This can result in a loss of product or an increase in reprocessing costs.
When the pulp density is below specification, there is an increase in the amount of carrier juice. Carrier juice is pasteurized along with the pulp and returned to the primary juice stream. Because it is pasteurized along with the pulp, it is often “overpasteurized” leading to quality and organoleptic degradation of the juice.
Should the concentration of pulp be too high, pressure limits within the pulp pasteurizer may be exceeded as well as proper feeding of the pulp pasteurizer can occur. Often this will create a blockage within the pulp pasteurizer and/or cause the temperatures within the pulp pasteurizer to fall out of specification preventing proper sterilization. This may result in either the loss of product or lower capacity.
Current methods to address these problems involve taking spot samples of the pulp discharge from the pulp concentrator and measuring the pulp concentration. Changes may then be made to the process to correct out of specification feed to the pulp pasteurizer.
One such measurement method is the grams/liter test, where a liter of pulp is mixed with a liter of water and put through a screening device to separate the water from the pulp. The remaining pulp on the screen is then weighed to determine the density.
Another measurement method is the quick fiber analysis, where dryness of the pulp is determined based on the free liquid that is removed without the application of pressure. For example, 200 grams of pulp sample are mixed with about 200 milliliters of water and stirred for a minute. This mixture sits for three minutes and is then stirred for another minute. The mixture is placed into a shaker with a 40 mesh screen for about three minutes and the liquid is retrieved from the sample. The liquid is measured in a graduated cylinder where the amount of liquid measured (in milliliters) is called the quick fiber. The total time is about 8-10 minutes, with even more time being needed for preparation.
As an alternative to the grams/liter test and the quick fiber analysis, pulp concentration may be measured using a nuclear magnetic resonance (NMR) sensor. U.S. Pat. No. 6,375,996, assigned to the present assignee, the disclosure of which is hereby incorporated by reference in its entirety, discloses obtaining a sample of the pulp, and measuring the pulp dryness using an NMR sensor.
Based on pulp concentrations in the sample measurements, manual adjustments may then be made to the pulp concentrator. In a screw type finisher, pulp concentration is changed by adjusting the finisher air pressure. In a paddle finisher, pulp concentration is changed by varying the speed of the paddle.
A disadvantage of performing the above described sample measurement approaches is that over time there may be wide variances in the pulp concentrations that can change even as pulp is being sampled and analyzed.